The present invention relates to a fuel consumption measuring apparatus for use with internal combustion engines which are fitted with electronic fuel injection, and more particularly relates to such an apparatus which is adapted to be fitted to an automobile.
Heretofore, it has been usual to measure the amount of fuel consumed by a vehicle by a fuel flow sensor provided in the fuel supply system.
Recently, fuel injection in vehicles has become common. In such vehicles, a new way of measuring fuel consumption has been proposed and practiced, as shown in FIG. 1 of the accompanying drawings as a block diagram. The electronically controlled fuel injection device shown herein comprises a detector 1 which detects intake air flow of the engine, detectors which are not shown and which detect other operating parameters of the vehicle, an arithmetic circuit 2 which calculates the proper amount or ideal amount of fuel to be injected into the engine--for example, in order to obtain a predetermined air/fuel ratio--and whose output is fed to a driving circuit 3, which changes it into a fuel injection control signal synchronized with the revolution of the engine, and corrected, and an electromagnetic fuel injection valve 4 which is operated by the fuel injection control signal.
The amount of fuel actually injected by the fuel injection valve 4 is not actually equal to the amount of fuel which is indicated by the control signal from the driving circuit 3 as proper to be input, because of operational time delay of the valve 4, and other sources of error therein. However, these various sources of error are measured in advance, and the driving circuit 3 is so constituted as to correct the fuel amount signals fed to it from the arithmetic circuit 2, so as to allow for these sources of error. In other words, the signal 2a from the arithmetic circuit 2 indicates the amount of fuel to be ideally supplied to the engine, and this is adjusted in the driving circuit 3 so as to counteract the errors which will be introduced in the operation of the fuel injection valve 4. Thus the signal 3a output from the driving circuit 3 to the fuel injection valve 4 does not directly indicate the exact amount of fuel to be injected, but rather is such as to cause the injection of the correct amount of fuel, bearing in mind the particular characteristics of the fuel injection valve 4.
The prior art fuel consumption system has comprised passing the fuel injection valve control signal 3a into a counting or totalling circuit 5 and measuring therein the amount of fuel consumed, outputting the result to a signal processing circuit 6 which calculates such data, for example, as the ongoing fuel consumption per kilometer therefrom, and which displays the result on a display unit 7. However, because the signal 3a does not directly represent the amount of fuel injected by the fuel injection valve 4, as explained above, because it has been corrected by the driving circuit 3 in anticipation of errors which will be introduced by the operation of the fuel injection valve 4, it is necessary first to pass this signal 3a through a correction circuit 8, before inputting it to the totalling circuit 5. This correction circuit 8, effectively, undoes the correction work done by the driving circuit 3, and restores the value denoted thereby to the value denoted by the signal 2a as the ideal amount of fuel to be supplied to the engine.
This correction and recorrection introduce error, clearly, and the circuit construction is rather complicated.